It is proposed to synthesize bisubstrate analogs of ATP and thymidine, as well as various pyrimidine analogs in substitution for thymidine, designed for potential inhibition of thymidine kinase and/or thymidylate kinase with the objective of inhibition of the replication of neoplastic cells and DNA-viruses. The merit of bisubstrate analogs relative to conventionl mononucleoside analogs is their theoretical enhanced potency, selectivity of locus of attack, and probably lack of mutagenic or carcinogenic potential. Preliminary data indicate not only the feasibility of their synthesis but also that they do indeed have inhibitory potential.